I've had a Force 4 (fiberglass) for a year and a half. I'm 5'11" and 165 pounds. I have kayaked about 6 years. I use a Greenland paddle and kayak mainly in the open ocean off Cape Cod. I've paddled the Force 4 for about 25 day trips in the ocean (usually 15-20 miles, a few of 30 miles), one two-day camping trip, and occasional rolling/skills practice sessions in a pond. I can't compare the Force 4 with other kayaks, because the only other kayak I've used in lots of different conditions is my first kayak, a WS Cape Horn 150. But here are my impressions of the Force 4 for anyone considering it.
I can summarize my feeling about the kayak (and kayaking) by saying that every time I get settled in the foot pegs and back-band and take the first stroke forward into the ocean, I think, "I love my kayak". The quality and workmanship on my boat are excellent. When shopping for boats, I did see a kevlar Force 4 with a small area on the hull where the gel coat failed to cover the cloth - it was not being sold as a second, and the dealer appeared surprised by the problem (genuinely, I think). I was bothered enough by this lapse in quality control by Impex and/or the dealer that I made a point of buying my boat from another dealer, and checked it out especially carefully.
Overall, I like the seat and backband in the boat and feel very comfortable even when in the seat continuously for 7 hours. On my first couple of trips, it seemed to me that the seat had too much of a backward tilt. So I took the seat out, removed the two-three inch thick foam that was under the front edge of the seat and replaced it with a thin piece of minicell so that the seat is angled more forward. With this simple fix, I find the seat and backband very comfortable. The backband is an Immersion Research (Reggie model, I think). A weakness is that the ratchet mechanism is easily unlocked when reaching behind the backband to grab something stowed behind the seat. Also, after a year of salt water exposure, there was some corrosion of the ratchets and they started slipping occasionally. I ended up putting small bolts through the adjustable straps to hold the band at a fixed length.
The boat has molded-in thigh brace areas, not enough by themselves to get a good purchase for a hip snap but perfect for glueing additional minicell thigh braces. I did this and feel perfectly locked in for bracing and rolling, with plenty of room in the hips for good torso rotation. I could be bigger and still fit well in boat. Cockpit is big enough that at 5'11" I can re-enter butt first easily.
I don't have enough experience with other boats to evaluate the handling of this boat in comparison. But I can say that I love the handling of the boat. When aggressively edged (very natural with a Greenland paddle), the boat turns very nicely, especially with an extended paddle sweep. I often paddle with a friend who uses a Nordkapp LV or an Anas Acuta using a Euro paddle. Of the three boats, the Anas Acuta clearly turns more easily, but even in tight quarters in rocks, I've never felt at a real disadvantage - just need to edge a little more and use extended paddle strokes when there's room. I used the boat for a class in Woods Hole, practicing bow rudder eddy turns, and it worked fine. I've used it for many sessions practicing in surf where I need to get swiveled around pointing into the waves in a hurry. I'm sure that boats with more rocker would do this more easily, but I've never found myself thinking "I wish this boat would turn more easily."
I find the boat very stable. When stopping to eat or pee at sea, I feel very comfortable pulling the spray skirt and attending to business with the paddle stowed, in pretty much any size swell. By comparison, my friend's Norkapp LV and Anas Acuta sit lower in the water around the cockpit, and in the same conditions, he will often ship water into the cockpit with his spraydeck off. When we practice rescues in rough water, the Force 4 has a clear advantage in shipping less water while pumping than either the Nordkapp LV or Anas Acuta, for which this is a significant problem, especially for a self-rescue.
Overall, I find the Force 4 a perfect boat for the ocean paddling I've done with it, including trips with winds up to 20 knots and fairly big seas. If I could try an experiment with altering the hull of the boat, I would like to see the effect on handling of adding volume to the bow. Even when unloaded, when paddling into sizeable swell, the bow tends to drive into oncoming swell, while my friend's Nordkapp LV rides up more, which seems to be a little more efficient.
A change I would definitely suggest to Impex is to add bungies or perimeter lines immediately behind the cockpit (the back perimeter lines start fairly far back) to hold the paddle during a paddle-float self-rescue or to hold the paddle out-rigger style for additional stability when stopping to eat. There is a groove for the paddle shaft just behind the seat, which works great for self-rescues while just holding the paddle, but bungies would give more flexibility.
The skeg works fine. I don't use it much, only to reduce broaching with big following or quartering swells. A couple of times I have forgotten it was down when doing a beach landing: never any problem, the skeg just pushed back up on its own. It has never gotten stuck. My friend's Valley boats have gotten stuck skegs from pebbles from landings in the same conditions several times, so there seems to be some difference.
I suspect some leak into the cockpit, because after 3-4 hours in swell there is routinely 2-3 inches of water in the cockpit and it doesn't seem to depend on the newness of the sprayskirt or how carefully the skirt is mated to my drytop or drysuit (and happens even if I never rolled). It isn't enough to be annoying, so I've never tried to diagnose it. I suspect leakage through the skeg cable mechanism or around the bolts for the seat and/or foot peg tracks, but can't really rule out leakage through the spray skirt. Both main hatches and the dayhatch stay totally dry.
I read a lot on paddling.net about people who have had many different boats and who are still thinking about trading or buying another one. Probably it's partly my lack of experience with other boats, but there hasn't yet been a day on the water when I wished I had a different boat than the Force 4. At least for me, the Force 4 has a perfect combination of speed, stability in big seas, and maneuverability. The maneuverability is undoubtedly less than shorter or more rockered boats, but I've never felt limited by it even when following my friend in his Anas Acuta between rocks.
I love the boat for messing around with long-boat surfing or playing around in tidal races just as much for as for point to point paddling. I would recommend the Force 4 highly and it were ever stolen or smashed beyond repair, I would buy another one in a second.